1. Field of the Invention
The present invention relates to a fluid restrictor in a hydrostatic bearing.
2. Description of the Prior Art
Hydrostatic bearings are fluid film bearings used in applications where high static stiffness, high static load capacity, and low viscous drag are desired. Hydrostatic bearings derive their load capacity from externally pressurized fluid lubricant. The stiffness of a hydrostatic bearing depends heavily upon the type of fluid restrictor used.
A typical bearing comprises two members, one of which moves in or on the other. The inner member is generally a shaft, or the like; the outer member may be a body member, bushing, sleeve, block or the like.
In conventional hydrostatic bearings, a bearing surface is provided with a plurality of pockets which are surrounded by a plurality of lands divided by discharge grooves. Pressurized fluid is supplied to these pockets through fixed orifice restrictors. The stiffness of orifice compensated hydrostatic bearings is greatly affected by clearance and fluid viscosity variations. Clearance variations are the natural result of a load being applied to the object which the bearing supports.
Other types of hydrostatic bearings utilize fixed laminar restrictors such as slot flow devices or capillary tubes to control stiffness. Such bearings are less stiff than the orifice compensated variety; however, their stiffness is greatly affected by clearance variations between the bearing and the object which it supports.
In an attempt to solve the difficulties resulting from the effects of clearance variations upon stiffness, numerus hydrostatic bearings have been developed which employ flow control valves to regulate flow in response to clearance variations. The performance of these flow control valves has been adversely affected by sticking, component inertia, and fluid viscosity variations.
At least one hydrostatic bearing has been developed utilizing an inherent variable fluid restrictor to regulate stiffness. Such an arrangement is disclosed in U.S. Pat. No. 3,754,799, dated Aug. 28, 1973, hereinafter referred to as the '799 patent. The fluid restrictor is located external to the bearing pocket in the '799 patent. In the common situation where the object supported by the bearing is tilted, the clearance variation is a function of axial position along the hydrostatic bearing. In this situation, the fluid restrictor and the bearing pocket will be exposed to different clearance variations. The inherent variation in flow through the fluid restrictor in response to a tilt load will not be appropriate for the clearance variation existing at the bearing pocket. The hydrostatic bearing disclosed in the '799 patent will not stabilize an object subjected to a tilt load.